> what kind of application would actually benefit from this?
Here's what I'm ideally picturing (though I think RAMster works for other environments too):
Individual machines are getting smaller and more likely to share external storage rather than have local storage. Cloud providers that are extremely cost conscious but can provide performance if paid enough (just as web hosters today offer a virtual server vs physical server option, the latter being more expensive).
Picture a rack of "microblades" in a lights-out data center, no local disks, labor-intensive and/or downtime-intensive to remove and upgrade (or perhaps closed sheet-metal so not upgradeable at all), RAM maxed out (or not upgradeable), some kind of fabric or mid-plane connecting blades in the rack (but possibly only one or two GbE ports per blade).
> but throughput will be much lower
There isn't a high degree of locality in swap read/write so readahead doesn't help a whole lot. Also, with RAMster, transmitted pages are compressed so less data is moved across the wire.
> Have you actually categorized the performance of RAMster vs spinning disk vs SSD?
Yes, some, against disk not SSD. RAMster is just recently working well enough.